Make sure bash snippets use -e

Using a bash shebang without any parameter or just -x discards -e which
bails out the build whenever something errors out.

jsduck: ignore the grep command exit code by wrapping it up with set +e
and set -e.  Tested on VisualEditor-jsduck.

Change-Id: I77ea8e45c1af6a5352bd61a0b4f4828c83e9e63d
Fix up qunit cleanup by using a publisher

The qunit-querystring has been made to run with -e which would abort the
build step if it fails, failling to garbage collect the symlink in
/srv/localhost/qunit.

By using the publisher 'postbuildscript', we ensure we delete the file
regardless of the build result.

Change-Id: I2831c6b8a998fd276e6139c24159cfcafb953bc6